Various means are used to this end. One can, for instance, apply the extremity of two bands one onto the other and weld them by passing electric current between two knurls moving transversally.
But, in some cases, both bands must be butt-welded so as not to produce excessive thickness. Both extremities, respectively downstream and upstream, of both bands must be shorn off, along two perfectly parallel lines, then brought closer to one another so that the opposite edges contact each other, thus producing a flash welding.
Such an installation therefore comprises various tools working successively and arranged, generally, one after the other along a longitudinal running direction of the bands.
First of all, the extremities, respectively downstream and upstream of the first and of the second bands are shorn off by a cutting tool which can advantageously comprise two shears working simultaneously and spaced by a constant distance in order to perform, at the extremities of both bands, two perfectly parallel edges, whereby both bands are maintained, as they are shorn off, by clamping grips mounted on a fixed frame.
Then, both shorn off edges are brought closer to one another and flash welded. During this operation, both extremities are maintained in clamping grips and, generally, a so-called cantilever distance is left between each pair of clamping grips and the corresponding edge to allow the welding operation to take place.
Moreover, it is necessary to apply the extremities of both bands one upon the other under a certain pressure in order to produce a forging effect during welding.
To this end, it is therefore used a welding machine comprising two pairs of clamping grips linked to a source of electric current and mounted, respectively, on a fixed frame and on a mobile frame moving longitudinally with respect to the fixed frame in order to bring both bands and the welding forging closer to one another.
However, the welding bead forms, on both faces of the band, fatty pads which must be eliminated so as not to disturb the passage of the welded section in the different sections of the processing machine. This is the reason why the machine usually comprises a tooling for flattening the welded spot consisting, most of the time, of a planing machine provided with knives to eliminate the beads, by transversal displacement along the welded spot.
Besides, the machine is provided with a number of auxiliary devices, for instance one or several looping devices giving a certain freedom to longitudinally displace each band without acting on the running means, centring means for perfect alignment of both bands, as well as a notching device in order to eliminate the extremities of the welded spot on the lateral edges of both bands, especially when the latter are not identical in width.
Such installations are therefore rather complicated and very cumbersome, whereas the toolings are usually located one after the other according to the order of operations to be performed.
In order to simplify the operations, it has already being suggested to associate the cutting tooling to the welding machine.
In such a case, the extremities of both bands must be clamped in both pairs of clamping grip before being shorn off, then one must release the grips in order to adjust the cantilever distances, tighten the grips again, adjust the distance between the opposite edges and proceed to the welding while exerting a forging pressure.
Then,both welded bands must be moved to the flattening tooling which also comprises clamping means in order to maintain the welded bands during the planing operation.
All these operations must be performed with great accuracy, for instance, by placing distance adjustment blocks between the extremities of both bands.